The present invention relates to stimulation systems, for example, spinal cord, peripheral, and deep-brain stimulation systems. A spinal cord stimulation system is an implantable pulse generating system used to provide electrical stimulation pulses from an electrode array placed epidurally or surgically near a patient's spine. An implanted pulse generator (IPG) may operate independently to provide the required electrical stimulation, or may interact with an external programmer, which delivers programming and/or control information and/or energy for the electrical stimulation, typically through a radio-frequency (RF) or other wireless signal.
Spinal cord stimulation (SCS) is a well accepted clinical method for reducing pain in certain populations of patients. SCS systems typically include an implanted device, lead wires, and electrodes connected to the lead wires. The implanted device receives signals from an external programmer, and transmits corresponding electrical pulses that are delivered to the spinal cord (or other tissue) through the electrodes which are implanted along the dura of the spinal cord. In a typical situation, the attached lead wires exit the epidural space and are tunneled around the torso of the patient to a subcutaneous pocket where the device is implanted.
Spinal cord and other stimulation systems are known in the art. For example, in U.S. Pat. No. 3,646,940, there is disclosed an implantable electronic stimulator that provides timed sequenced electrical impulses to a plurality of electrodes so that only one electrode has a voltage applied to it at any given time. Thus, the electrical stimuli provided by the apparatus taught in the '940 patent comprise sequential, or non-overlapping, stimuli.
In U.S. Pat. No. 3,724,467, an electrode implant is disclosed for the neurostimulation of the spinal cord. A relatively thin and flexible strip of physiologically inert plastic is provided with a plurality of electrodes formed thereon. The electrodes are connected by leads to an RF receiver, which is also implanted, and which is controlled by an external controller. The implanted RF receiver has no power storage means for generating electrical stimulations, and must be coupled to the external controller in order for neurostimulation to occur.
In U.S. Pat. No. 3,822,708, another type of electrical spinal cord stimulating device is shown. The device has five aligned electrodes which are positioned longitudinally on the spinal cord and transversely to the nerves entering the spinal cord. Current pulses applied to the electrodes are said to block sensed intractable pain, while allowing passage of other sensations. The stimulation pulses applied to the electrodes are approximately 250 microseconds in width with a repetition rate of 5 to 200 pulses per second. A patient-operable switch allows the patient to change which electrodes are activated, i.e., which electrodes receive the current stimulus, so that the area between the activated electrodes on the spinal cord can be adjusted, as required, to better block the pain.
Other representative patents that show spinal cord stimulation systems or electrodes include U.S. Pat. Nos. 4,338,945; 4,379,462; 5,121,754; 5,417,719, 5,501,703, and 6,516,227. All of the patents noted above are hereby incorporated by reference.
A typical IPG is self contained, having a multi-year battery pack and a single treatment program, and is generally programmed during or immediately following implantation in the patient's body.
Other SCS systems have no implanted power source, but receive power and programming and/or control information from an external transmitter. These systems will convert the RF signals from the transmitter to provide power to the implanted receiver, and use the RF programming information to determine the intensity, location, and duration of the electrical pulses delivered to the electrodes.
In either case, before the IPG can be properly programmed, stimulation thresholds must be determined so that the pulse stimuli the IPG delivers is strong enough to effectively treat the patient, but not so strong that the treatment is uncomfortable or painful for the patient.
Unfortunately, this process is generally inconvenient and time consuming for both the patient and the professional performing the threshold determination. For example, typical systems start each electrode amplitude at zero and ramp linearly until a maximum tolerance is determined. In some known cases, this process is shortened by only determining a small number of the lead electrode parameters, and estimating or guessing proper parameters for the remaining electrodes. This method can lead to ineffective or uncomfortable treatments.
There is, therefore, a need in the art for a system, process and device for improved IPG calibration techniques.